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AC & DC Coupled Solar Battery Systems

With the proliferation of solar storage throughout the industry we thought it would be a good idea to take a look at the difference between AC & DC coupled solar battery systems. There is a good chance you have heard of AC and DC electricity before but you might not be aware of what these terms actually mean.

DC stands for Direct Current and much like the name implies this is when the electrical current flows in one direction only. AC, or Alternating Current, has the electrical current moving back and forth from the source to the destination such as an appliance. While AC is the standard for Australian power networks solar panels actually produce DC power.

So if our solar panels are producing DC power how does our home or business turn it into AC power so we can use it? The simple answer is your solar inverter which as the name suggests takes the DC power from your panels and inverts it to AC power for your home. However when it comes to solar batteries the most efficient method of storage is to use DC power.

The Different Types Of Solar Battery Systems

Solar battery systems can be set up for both off-grid and grid-tied setups. An off-grid solar system is completely isolated from the traditional power grid, generating all the power it needs for the home or business through alternative power sources like solar. We recently carried out an off grid solar system upgrade for footy legend Nick Cummins so check that out if you want to know more about off-grid solar.

A grid-tie solar system is when your home is also connected to the traditional power grid to both feed in excess power and draw from it should the battery not have any charge left in the evening. This is what most homes and offices across Australia are running and while the vast amount of instals we carry out are to grid tied homes, off grid is surging in popularity.

DC Coupled Solar Systems

DC coupled battery systems have been used for a long time now in both off-grid solar and smaller capacity systems such as those you might find on a boat or camper. While recent advancements in inverter technology have led to the emergence of AC storage solutions DC still shines in certain applications.

In a DC coupled off-grid solar system you will typically use what we call “solar charge controllers” in order to charge your batteries with power directly from the solar panels. From this point the battery will feed into a multi-mode inverter so the power can be used by your home and its appliances. As no conversion happens before storage you get the best efficiency possible for charging your battery.

In larger installations a solar charge controller with maximum power point trackers (MPPT) are used in order to increase efficiency and allow operation at higher string voltages. When using MPPT the charging of a DC coupled system can achieve up to 99% efficiency. By adding more controllers we can also add more solar panels which makes DC coupling quite modular.

dc coupled solar power system diagram

AC Coupled Solar Systems

AC Coupled solar systems use a more common string solar inverter that is paired with a multi-mode inverter to charge the battery. The advantage here is that the panels deliver the power to the string inverter which then passes it along to your home for your appliances to use which makes it great for powering high AC loads during daylight.

Any excess power is directed to the battery which makes this extremely setup shine if power demand is at its highest during the day. Because we are using strong inverters here we can install much larger solar arrays without having to use more MPPT charge controllers which makes it a bit cheaper than DC coupled systems above 6kW.

While an AC coupled system will give us much better efficiency with higher AC loads during the day it does result in a lower power charging efficiency for the battery. It does present more flexibility when it comes to multiple string inverters and with more and more of these coming with dual MPPT inputs we can have different strings of panels installed for maximum capture.

ac coupled solar power system diagram

Thinking About Going Off Grid?

RedEarth has developed the “Storage Solution Calculator” which can generate the perfect solar storage solution based on your individual usage patterns. It only takes moments to get everything you need to make the most informed decision possible.
Off-Grid System Calculator

AC Coupled Batteries

For those with grid tied homes, AC batteries have become a welcome innovation in the energy storage market due to their simplicity and versatility. As they are able to be charged via AC they slot easily into any existing solar power system and present an economical way to upgrade the savings potential of your solar setup.

The reason they can be easily slotted into any existing AC system is due to the fact the battery itself is bundled in with an inverter/charger and battery management system all in one unit. They are also modular so you can add to your solar power storage as you see fit which adds a touch of flexibility that we appreciate. Examples of AC batteries include the Tesla Powerwall 2.

ac coupled battery diagram

DC Coupled Hybrid

You may have heard the term hybrid before in reference to solar inverters and this is another way of describing DC coupled solar battery systems. Hybrid inverters are best thought of as an all-in-one solution, coming packed with battery inverter/chargers and high voltage MPPT controllers. They come with the added benefit of being able to support higher voltage battery systems.

Having one unit that takes care of everything while giving you a best of both worlds scenario for grid tied homes, hybrid systems are compact, economical and have the same high efficiency battery charging as a normal DC coupled setup. There are more and more hybrid inverters making their way onto the market which means consumer choice is also a plus.

dc coupled hybrid diagram

Want To Know What Works Best For Your Needs?

There are many things to consider when looking to take up solar and whether your system will be AC or DC coupled is certainly one of them. The best configuration for you will depend on whether your home or business is off grid or not as well as several other factors such as the need for expansion in the future and when the property needs power the most.

Both offer different advantages, DC coupled systems have better battery charge efficiency and can be added to for generally less outlay than the AC counterparts. AC coupled systems are better for handling heavier business and household energy needs during the day and the use of string inverters means they can operate with higher DC voltages should more solar arrays be added.

The best way to establish what will deliver the best results for your needs is to talk with a professional solar consultant. Our consultants are experienced in the solar industry and understand what works and what doesn’t. Our goal is to find the right solar power system for you so that you can reap the most benefits possible.

If you would like to talk to one of our solar consultants about AC and DC coupled systems or would like to know more information about anything related to solar, give us a call on 1800 255 474. You can also fill in our quick quote form to have us get back to you at a time that suits to discuss any solar needs you have.

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